Medieval agriculture in northern Europe fed, clothed and sheltered a predominantly rural society with a much lower population density than it is today.
北欧的中世纪农业为主要的农村社会提供了食物、衣服和庇护,人口密度比今天低得多。
2
The Moon's mean density is much lower than that of Earth but is about the same as that of Earth's mantle.
月球的平均密度比地球低得多,但与地球的地幔密度大致相同。
3
Salt has lowerdensity than the surrounding rock, so it tends to flow upwards, pushing up the overlying layers of rock to form a dome.